This invention relates to a flexible disk drive for carrying out data recording and reproducing operations to and from a rotating disk-shaped magnetic recording medium of a flexible disk and, in particular, to an arrangement structure for a Hall element for generating an index signal.
In the manner which is well known in the art, the flexible disk drives (which may be hereinafter called xe2x80x9cFDDsxe2x80x9d for short) of this type are devices for carrying out data recording and reproducing operations to and from disk-shaped magnetic recording media of the flexible disks (which may be hereinafter called xe2x80x9cFDsxe2x80x9d for short) loaded therein. In addition, such flexible disk drives are widely mounted or loaded in electronic devices such as a personal computer, a work station, a word processor, or the like.
Loaded in the flexible disk drive, the flexible disk is rotated by a motor. An index signal is used to determine a starting position of the rotating flexible disk. That is, the index signal is a pulse signal that is generated each time the disk-shaped magnetic recording medium in the flexible disk makes one revolution. For example, the index signal is used for generation of a xe2x80x9cReadyxe2x80x9d signal in the FDD. The xe2x80x9cReadyxe2x80x9d signal is a signal for notifying the system that writing/reading can be prepared and is generated by detecting that the disk-shaped magnetic recording medium or the motor is rotated by means of the index signal. In the system, the index signal is referred on starting of writing on track formatting, and the index signal is used for determining a point for stopping after one revolution. The index signal is used for management of processing time on writing and on reading. For example, a predetermined count is preliminarily defined and processing is made as an error if the processing for a designated sector is not carried out until counting the number of pulses of the index signal up to the predetermined count on writing/reading.
In order to generate such as an index signal, in an FDD for driving an FD of 5.25 inch type (which will be hereinafter called xe2x80x9cFDD of 5.25 inch typexe2x80x9d), an index hole bored in a flexible disk is used. More specifically, generation of the index hole was carried out by irradiating light beam through the index hole bored in a jacket or a cartridge and by detecting presence of the index hole by the light beam.
On the other hand, in an FDD for driving an FD of 3.5 inch type (Which will be hereinafter called (FDD of 3.5 inch type) which becomes presently mainstream, there is no index hole in the flexible disk. In the FDD of 3.5 inch type, driving of the flexible disk is carried out by rotating a driving pin projecting from a disk table (chucking table) toward the flexible disk. It is therefore possible to rotatably position among the disk table, a rotor of the motor, and the flexible disk. As a result, it is possible to detect rotation of the flexible disk by looking over rotation of the disk table or the rotor.
In particular, in a flexible disk drive where a DD (direct-drive) motor such as a spindle motor is used for rotatably driving the flexible disk, the index signal is generated on the basis of operation in periphery of a rotor of the DD motor. More specifically, a notch portion is partially provided with a peripheral side surface of a disk-shaped casing composing the rotor while a magnet is disposed inside the casing so that only one magnetic pole (e.g. a north pole) is visible via the notch portion. Such a magnet is called an index detection magnet. In addition, on a main frame on which a stator of the DD motor and so on are mounted, a main printed wiring board on which a predetermined circuit is formed is disposed. A Hall element is located on the main printed wiring board at a predetermined position corresponding to the outside of the rotor. The Hall element is called an index detection Hall element.
Herein, the Hall element is a semiconductor element applying a Hall effect. The Hall element is a phenomenon where an electric field occurs in a conductor in a y-direction perpendicular to both of an x-direction and a z-direction when the electric current flows in the x-direction in the conductor and when the magnetic field is applied to the z-direction perpendicular to the x-direction. The electric field caused thereby is a Hall electric field and an output of the Hall element in response thereto is a Hall output.
In addition, Hall elements are used not only as the index detection Hall element but also for detecting a position in the rotor of the spindle motor. Such Hall elements are called position detection Hall elements. A spindle motor using the position detection Hall elements is called a Hall motor.
In the manner which is described above, in prior art, a single-pole magnetized magnet is used as the index detection magnet. It is difficult to obtain a stable generation timing for the index signal. Accordingly, in order to obtain the stable generation timing for the index signal, the co-inventors of the present invention have already proposed and filed an application to use, as the index detection magnet, a double-pole magnetized magnet (that is, one where a south pole and a north pole are put side by side) (see Japanese Unexamined Patent Publication Tokkai No. 2001-190,055 or JP-A 2001-190055).
In addition, the index detection magnet mounted on the rotor and the index detection Hall element located on the printed wiring board are disposed so that they are apart from each other at a magnetic field detection position by a little distance. The printed wiring board is disposed so as to extend in a direction normal to a rotation axis of the spindle motor. Accordingly, a conventional index detection Hall element necessarily has a magnetic detection surface which is disposed to extend in parallel with a direction of the magnetic field generated by the index detection magnet. Therefore, the conventional index detection Hall element is disadvantageous in that it has a poor sensitive condition for the magnetic field.
On the other hand, in order to improve the sensitive condition for the magnetic field, it may be devised to use, as the index detection Hall element, a specific Hall element having a magnetic field detection surface extending in a lateral direction (namely, at a side surface instead of an upper surface) thereof. However, inasmuch as the specific Hall element is not generally commercially available and is a specific and rare one, it is disadvantageous in that cost rises.
It is therefore an object of the present invention to provide a flexible disk drive which is provided with an index detection Hall element having an improved detection sensitive condition for a magnetic field.
Other objects of this invention will become clear as the description proceeds.
On describing the gist of an aspect of this invention, it is possible to be understood that a flexible disk drive comprises a main frame in which a flexible disk is inserted. The main frame has a frame main surface and a frame back surface. Mounted on the frame main surface of the main frame, a motor rotatably drives the flexible disk inserted in the main frame. The motor has a rotation axis. The motor comprises a rotor rotatably disposed around the rotation axis and a stator combined with the rotor. The rotor has an external peripheral side surface on which an index detection magnet is mounted. Mounted on the frame back surface of the main frame, a circuit board mounts a control circuit for carrying out a driving control of the motor thereon. According to the aspect of this invention, the above-understood circuit board comprises a main circuit board for mounting the control circuit thereon and for extending in a direction perpendicular to the rotation axis of the motor and a sub circuit board mounted to said main circuit board at a position close to the external peripheral side surface of the rotor so as to extend in a direction in parallel with the rotation axis of the motor. Attached on the sub circuit board, an index detection Hall element has a magnetic field detection surface which is disposed so as to oppose to the external peripheral side surface of the rotor.
In the above-mentioned flexible disk drive, the sub circuit board has a board main surface opposed to the rotor and a board back surface opposite to the board main surface. The sub circuit board may have a penetration for penetrating between the board main surface and the board back surface. In this event, the index detection Hall element may preferably be inserted in the penetration so that the magnetic field detection surface is faced to the board main surface of the sub circuit board. The main circuit board may have an edge close to the rotor. In this event, the sub circuit board may desirably be attached to the main circuit board at the edge of the main circuit board. The board back surface of the sub circuit board may serve as a soldering surface. In this event, the sub circuit board and the main circuit board may preferably be soldered with each other at the soldering surface with the board back surface of the sub circuit board and the edge of the main circuit board in contact with each other. The index detection Hall element may have terminals electrically connected to the soldering surface.